Mbh 9.42.2a

Vaishampayana said, "A great enmity arose between Vishvamitra and Vasishtha, O Bharata, due to their rivalry in respect of ascetic austerities. The high abode of Vasishtha was in the tirtha called Sthanu on the eastern bank of the Sarasvati. On the opposite bank was the asylum of the intelligent Vishvamitra. There, in that tirtha, O monarch, Sthanu (Mahadeva) had practised the austerest penances. Sages still speak of those fierce feats. Having performed a sacrifice there and worshipped the river Sarasvati, Sthanu established that tirtha there. Hence it is known by the name Sthanu-tirtha, O lord. In that tirtha, the celestials had, in days of yore, O king, installed Skanda, that slayer of the enemies of the gods, in the supreme command of their army. Unto that tirtha of the Sarasvati, the great Rishi Vishvamitra, by the aid of his austere penances, brought Vasishtha. Listen to that history. The two ascetics Vishvamitra and Vasishtha, O Bharata, every day challenged each other very earnestly in respect of the superiority of their penances. The great Muni Vishvamitra, burning (with jealousy) at sight of the energy of Vasishtha, began to reflect on the matter. Though devoted to the performance of his duties, this, however, is the resolution, O Bharata, that he formed: 'This Sarasvati shall quickly bring, by force of her current, that foremost of ascetics, Vasishtha, to my presence. After he shall have been brought hither, I shall, without doubt, slay that foremost of regenerate ones.' Having settled this, the illustrious and great Rishi Vishvamitra with eyes red in wrath, thought of that foremost of rivers. Thus remembered by the ascetic, she became exceedingly agitated. The fair lady, however, repaired to that Rishi of great energy and great wrath. Pale and trembling, Sarasvati, with joined hands appeared before that foremost of sages. Indeed, the lady was much afflicted with grief, even like a woman who has lost her mighty lord.